Catalytic method of producing aromatic compounds



Patented June 10, 1947 CATALYTIC METHOD OF PRODUCING AROMATIC COMPOUNDS James Kenneth Dixon, Riverside, Conn., assignor to American Oyanamid Company, New

York,

N. Y., a corporation of Maine No Drawing. Application August 21, 1945, Serial No. 611,927

11 Claims.

This invention relates to the production of aryl compounds having at least one aliphatic nuclear substituent which contains a carbon-tocarbon double bond, and more particularly, to the production of such aryl compounds as those which have a vinyl group attached to an aryl nucleus.

The patent of Murray Gray Sturrock and Thomas Lawe No. 2,373,982 which issued April 17, 1945, discloses a method of producing styrenes and other aryl compounds made in accordance with the present invention, and this patent deals with the use of siliceous catalysts, and more particularly, hydrated aluminum silicate catalysts.

An object of the present invention is to provide improved catalysts which are efiective for the conversion of diaryl substituted paraflins, having at least two carbon atoms in the paraffin chain and having the aryl groups attached to the same carbon atom, into two aromatic compounds, including one which has an aliphatic nuclear substituent containing a carbon-to-carbon double bond.

This and other objects are attained by employing a zirconia modified aluminum silicate catalyst for the aforementioned type of reaction. Thus the present process contemplates contacting a vapor comprising a compound of the class consisting of parafflns having at least two carbon atoms and having two aryl substituents attached to one of said carbon atoms, and their nuclear substituted derivatives, with a silicate catalyst which comprises alumina and zirconia at a temperature of at least 350 C. and preferably at a temperature of about SOD-600 C. It is preferable that the contact time be less than 0.4 second and in order to avoid practical difiiculties it is generally desirable to employ a contact time of 0.001 second or more. Still another feature of the present process is the use of a diluent, preferably water vapor in relatively high proportions, namely from about to 15 or more .mols of diluent per mol of the diaryl substituted paraffin. Water vapor is one of the most desirable diluents since it may be easily condensed and thereby separated from the final product.

The following examples in which the proportions are in parts by weight are given by 'way of illustration and not in limitation. The jditolylethane employed in the following examples is 1,1-

di-p-tolylethane.

Example 1 About 400 parts of a silica-alumina-zirconia catalyst (catalyst "A) are packed into a tube which is heated and maintained at a temperature -of about 376-386 C. Ditolylethane is passed through the tube at a rate of 2210 parts per hour and water vapor is admixed therewith before it is passed through the tube and fed at the rate of about 2930 parts per hour. A contact time of about 0.1 second is employed. A total of about 2580 parts of ditolylethane are passed through the tube and about 2500 parts of hydro- -carbon condensate are recovered. The condensate is distilled to yield about 730 parts of a light oil boiling below 200 C., 1700 parts of hydrocarbon boiling at about the boiling point of ditolylethane and containing the unchanged ditolylethane together with small quantities of other substances such as 1,1-ditolylethylene, leaving a residue of about 60 parts of a high boiling material and leaving a distillation loss of about 10 parts of the compound.

The light oil is titrated with a potassium bromide-bromate solution and the proportion of p-methylstyrene in the light oil is calculated from the results of this titration (assuming the unsaturated content is all p-methylstyrene). Since it is theoretically possible to have only about 56.2% of p-methylstyrene in the light oil the percentage of p-methylstyrene found by the above analysis when subtracted from 56.2 gives the percentage of p-ethyltoluene in the light oil.

. The remainder of the light oil is assumed to be toluene. The foregoing method of analysis and calculations have been found to be accurate when checked by the results obtained by fractionation of the light oil, by infra-red and other spectroscopic analyses thereof. Using the foregoing method of analysis the light oil obtained in accordance with this example contains about 220 parts of p-methylstyrene, 88 parts of p-ethyltoluene and 422 parts of toluene.

The p-methylstyrene, the toluene and the pethyltoluene mayeach be separated from the light oil by fractionation. The ethyltoluene may be dehydrogenated to form p-methylstyrene. The unreacted ditolylethane may be recycled through the reaction tube in the same manner as described above in connection with the original pass of the ditolylethane. By recirculating the Example 2 400 parts of a silica-alumina-zirconia catalyst (catalyst "A) are packed into a tube, heated and maintained at about 527-565 C. Ditolylethane is passed through the tube at the rate of about 1560 parts per hour and admixed therewith,

water vapor is passed through the tube at the rate of 3730 parts per hour. A contact time of about 0.1 second is employed. A total of about 2620 parts of ditolylethane is passed through the tube and about 2550 parts of hydrocarbon condensate are recovered. The condensate is distilled to yield about 440 parts of a light oil boiling below 200 C., 2050 parts of hydrocarbons boiling at about the'boiling point of ditolylethane and containing, the unchanged ditolylethane together with small quantities of other substances such as asymmetric ditolylethylene, leaving a residue of about 60 parts of high boiling material.

The light oil contains 180 parts of p-methylstyrene, 33 parts of p-ethyltoluene and 227 parts of toluene when analyzed according to the method described in Example 1. The light oil may be separated into its constituents by any desired method such as fractionation.

Example 3 About 50 parts of a zirconia-alumina-silica catalyst (catalyst A) are packed into a converter tube, heated and maintained at a temperature of about 548-560 C. Ditolylethane is passed through the tube at the rate of about 1370 parts per hour together with water vapor at the rate of 2100 parts per hour. A contact time of about 0.01 second is employed. A total of about 2650 parts of ditolylethane is passed through the tube and about 2640 parts of hydrocarbon condensate are recovered. The condensate is distilled to yield about690 parts of a light oil boiling below 200 C., 1890 parts of a hydrocarbon fraction boiling at about the boiling point of ditolylethane and containing the unchanged ditolylethane together with small quantities of other hydrocarbons such as asymmetric ditolylethylene, leaving about 20 parts of a high boiling residue and leaving a distillation loss of about 40 parts of the condensate.

Upon analysis of the light oil using the method described in Example 1 it is found to contain 345 parts of p-methylstyrene, 21 parts of p-ethyltoluene and 324 parts of toluene.

1 Example 4 A contact time of about 0.016 second is 2510 parts of hydrocarbon condensate are recovered. Upon distillation ofthe hydrocarbon condensate about 940 parts of a light oil boiling below 200 C., 1500 parts of hydrocarbons boiling at about the boiling point of ditolylethane and containing the unchanged ditolylethane and 50 parts of high boiling residue are ,obtained, leaving a distillation loss of about 20=parts of condensate.

The light oil may be analyzed in accordance About 425 parts of Na2SiOa.9H2O are dissolv'ed in about 1500 parts of water and dilute sulfuric acid (about 20%) is added with vigorous agitation until the pH is about 6.5 and the resulting silica gel is then repeatedly washed, filtered and slurried until the washings no longer give a positive test for sodium by the magnesium uranyl acetate test. The washed silica gel is slurried in about 3000 parts of Water and 500 parts of an aqueous solution containing about 46.5 parts of KA1(SO4)2.12H2O and about 13.1 parts of ZrOCl2.8H2O are added and then the pH is brought to about 6.5 by the addition of 2MNH4OH and thereafter the gel is filtered, washed and reslurried repeatedly. When thoroughly washed the gel is dried and heated to about 700 C., and maintained at that temperature for about onehalf hour. The final product contains about S102, 5% A1203 and 5% ZrOz.

The zirconia modified aluminum silicate catalyst used in accordance with this invention may be prepared by coprecipitation of alumina, zirconia and silica to form a hydrogel which is thereafter washed and dried. Still another methof zirconia to alumina may be varied widely, but

in general, it is preferable that the silicates contain at least 1% by weight of A1203 and at least 1% by weight of ZrOz.

My catalyst may include other heat resistant and solid substances which activate them or which are entirely inert, and such substances may be used to extend the active surface of the zirconia modified aluminum silicate catalysts, or they may be used as supports for the catalysts. For example, the zirconia-alumina-silicate catalysts of this invention may be supported upon finely divided silicon carbide, non-porous aluminum oxide (such as those materials sold under the trade names Alfrax," Alundum, etc.) highly fired ceramic materials in the form of rings, saddles, grids and the like. Binding agents such as sodium silicate may be advantageously employed in some cases to improve the mechanical stability of my catalysts. I

My catalysts are employed in a finely divided condition fashioned into pellets which are preferably no larger than about 5 mm. in their greatest diameter. The pellets may be in any desired shape such as cubical, spherical, or of an irregular granular shape. When large pellets are emall of which are volatile at the temperature and pressure used in the process. Those substances containing tolyl, xylyl, cresyl, xenyl, monochlorolyst instead of passing therethrough in a uniform manner.

The converter into which the catalyst is packed may be a tube constructed of steel, silica or any other suitable material and in large scale opera! tions the converter may comprise a plurality of such tubes or it may be a shell-type converter having one or more layers or trays of catalyst therein.

A short contact time of the diaryl parafiin with the catalyst is desirable in carrying out the reactions in accordance with this invention. While longer contact times may be used if desired it is generally preferable that the contact time be less than 0.4 second. The contact times between about 0.1 and 0.05 are especially suitable. Generally it is desirable to employ a contact time of 0.001 second or longer, in order to avoid practical difliculties. The calculation of the contact of the Vapor with the catalyst is a complex matter, and in order to simplify this calculation I have used the term contact time" herein to mean those values which are computed on the assumption that the catalyst contains 50% voids and neglecting both the pressure drop through the catalyst and the increase in volume which occurs during the reaction. The contact time employed in the foregoing examples is about 0.1 second.

Inasmuch as the reaction is neither highly exothermic nor endothermic it is not necessary to supply much more heat than that necessary to compensate for conduction and radiation losses in order to maintain the reaction temperature of the vapors passing through the catalyst, pro-- viding that the vapors which are fed to the catalyst are preheated to about the desired reaction temperature and providing a high ratio of diluent to the diaryl paraflin is employed. I therefore prefer that the vapors fed to the catalyst be preheated to the reaction temperature. Any suitable method of heating the converter may be employed such as, for example, electrical resistance heaters. I

The following are illustrative of the aliphatic compounds having two aryl substituents attached to the same carbon atom thereof which may be converted into the mononuclear aromatic compounds in accordance with the present invention: 1,1-diphenylethane, each of the l-phenyl-ltolylethanes, each of the 1,1-ditolylethanes, each of the l-phenyl-l-xylylethanes, each of the 1- tolyl-l-xylylethanes, each of the 1,1-dixylylethanes, 1,1-diphenylpropane, each of the l-phenyll-tolylpropanes, each of the 1,1-ditolylpropanes, each of the l-tolyl-l-xylylpropanes, each of the 2,2-ditolylpr'opanes, each of the 1,1-di(monochlorophenyD-ethanes, each of the l,1-di-(dichlorophenyD-ethanes, each of the 1,1-di- (monohydroxy phenyl) -ethanes, each of the 1,1- dicresylethanes, each of the 2,2-dicresylpropanes, each of the 1,1-dinaphthylethanes, each of the 1,1-dixenylethanes, each of the l-tolyl-l-naphthylethanes, and the like and their nuclear substituted halogen, hydroxyl and other derivatives phenyl and dichlorophenyl groups may be attached to the carbon atom of the paraffin chain at the ortho, meta or para positions and when two of these groups are present they may be attached in the same or different positions.

The reaction temperature may be varied from about 350 C. up to about 600 C. or even higher in some cases. Temperatures above 600 C. cause some pyrolysis loss but on the other hand some of the diaryl paraflins are not easily decomposed at lower temperatures. It is particularly important to employ a short time of contact when temperatures in the neighborhood of 600 C. are

used in order to avoid an undesired amount of pyrolysis loss due to side-reactions. Among such side-reactions are those which lead to the formation of polynuclear compounds including anthracene derivatives.

One of the advantages of employing a short contact time with catalysts is that the life thereof is prolonged. With contact times of the order of 1 second or more the catalyst may become fouled in a relatively short period of time due to the deposition of carbonaceous materials on the surface of the catalyst. When it is necessary or desirable to reactivate the catalyst this may be done by passing heated air, preferably mixed with steam or carbon dioxide, through the catalyst. The temperature of the air and steam mixture should be raised to about 500-650 C. The air enables the carbon to burn whereas the steam or carbon dioxide which is used in conjunction with the air keeps the temperature from rising too high which might cause areduction in the activity in thecatalyst. Generally, at temperatures of about 500 C. the carbon begins to burn off and the heat of this reaction causes the temperature to rise to about 650 C.-without the application of any external heat.

It may be seen that the proximity of the reactivation temperature to the reaction temperature greatly simplifies the change from normal operation to reactivation and back to normal operation. Since the normal highly active life of the catalyst greatly exceeds the time required for its reactivation the operation of two or more converters in parallel is readily accomplished. The short time of reactivation enables one to keep one or more converters in normal operation while one or more other converters are being reactivated.

Any material which is volatile and which does not react with the diaryl substituted paraflin which is to be used in accordance with my process and which does not react with the products formed by the decomposition of the diaryl substituted paraflin may be used as a diluent. Among these some examples are: water, the hydr0carbons (such as benzene and toluene), the fixed gases (such as nitrogen and carbon dioxide), etcv Water vapor is the preferred diluent inasmuch as it may be readily condensed and therefore 7 diaryl substituted paraffin with the catalyst can be reduced to the desired point easily. It has been found that in order to obtain the short contact times which are desirable in accordance with th present invention the molal ratio of diluent to the diaryl substituted aliphatic compound in the feed to the catalyst is preferably between about :1 and 150:1, or more. If the feed can be supplied rapidly enough to provide a low contact time without the use of the large proportion of diluent the ratio of diluent to the diaryl substituted paraflin may be as low as 1:2.

It has been found that it is frequently desirable to convert only a few percent of the diaryl substituted paraffin fed to the catalyst in one pass but by recovering the unconverted diaryl substituted paraffin and recirculating it from one to five times or more, a high yield is obtained very economically.

My process may be operated at elevated or reduced pressure and under some conditions it may be particularly advantageous to operate under reduced pressure. If the diaryl substituted paraffin which is to be used in accordance with present processes is not readily volatile at ordinary pressure, reduced pressures may be used to facilitate the operation of my process.

The present process is a convenient and economical method of converting the diaryl sub-.

stituted paraflins, having at least .two carbon atoms in the parafiin chain and having the two aryl groups attached to the same carbon atom, into two aromatic compounds, one of which contains a side chain having an ethylenic group. The vinyl substituted aryl compounds prepared in accordance with the present invention have wide utility in the production of polymers which in turn are useful for molding, casting, laminating and for many other purposes. Furthermore, pure aryl compounds such as xylene in extremely high purity may be produced simultaneously with the production of the aromatic compound containing an ethylenic side chain. Thu when a diaryl substituted parai'lin is cracked in accordance with this invention one molecule of an aryl compound having an ethylenic side chain is obtained together with one molecule of a pure aryl compound which does not have an ethylenic side chain. Such pure aryl compounds, as for example pure m-xylene or pure p-xylene, find utility in the synthesis organic compounds where the presence of one or more of the possible isomers is undesired.

I claim:

1. A process of producing a plurality of arcmatic compounds which comprises heating a parafiin having at least two carbon atoms and having two aryl substituents attached to one of said carbon atoms at a temperature which will cause said paraffin to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least350 C., in the presence of a zirconia-alumina-silica catalyst.

2. A process of producing a'plurality of aromatic compounds which comprises contacting a substance selected .from the class consisting of parafiins having at least two carbon atoms in the paraffin chain and having two aryl substituents attached to one carbon atom thereof, and their nuclear substituted derivatives at a temperature which will cause said paraifin to decompose into a plurality of aromati compounds in the presence of a catalyst and which is at least 350 C., with zirconia-alumina-silica.

3. A process of producing a plurality of aromatic compounds which comprises mixing a substance selected from the class consisting of diaryl substituted paraffins having at least two carbon atoms in the paraffin chain and in which both aryl groups are attached to the same carbon atom and their nuclear substituted derivatives with a diluent contacting the resulting mixture thereof with a zirconia-silica-alumina catalyst and maintaining the temperature of said mixture at a temperature which will cause said paraffin to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C., during the time it is in contact with said catalyst.

4. A process as in claim 3 wherein the diaryl substituted paraffin has an asymmetric diarylethane and where the time of contact thereof with the catalyst is between about 0.001 second and about 0.4 second.

5. A process as in claim 3 wherein the diluent is water vapor.

6. In a method of producing a plurality of arcmatic compounds the steps of which comprise heating a substance of the class consisting of diaryl substituted parafiins having at least two carbon atoms in the paraflin chain and having both aryl groups attached to one of the carbon atoms, and their nuclear substituted derivatives; to a temperature which will cause said paraflin to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C. passing said substance through a zirconia-alumina-silica catalyst with a contact time of less than 0.4 second.

7. In a method of producting a plurality of aromatic compounds the step which comprises contacting an asymmetric ditolylethane with a zirconia-alumina-silica catalyst at a temperature which will cause said paraffin to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C.,

and for a contact time of less than 0.4 second.

8. In a method of producing a plurality of arcmatic compounds the step which comprises contacting a 1,1-di-xylylethane with a zirconia-alumi'na silica catalyst at a temperature which will cause said parafiln to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C., and for a contact time of less than 0.4 second.

9. Iii a process of producing a plurality of aromatic compounds, the step which comprises contacting an asymmetric diarylethane With a zirconia-alumina-silica catalyst at .a temperature which will cause said paraffin to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 0., and for a contact time of less than 0.4 second, said diarylethane having at least one aryl group substituted with an alkyl group. i

10. In a process of producing a plurality of aromatic compounds, the step which comprises contacting an asymmetric diarylethane with a zirconia-alumina-silica catalyst at a temperature which will cause said paraflin to decompose into a plurality of aromatic compounds in the presence of a catalyst and which is at least 350 C. and fora contact time of less than 0.4 second, said diarylethane having at least one aryl group substituted with-a hydroxyl group.

11. In a process of producing a plurality of aromatic compounds, the step which comprises contacting an asymmetric diarylethane with a, zirconia-alumina-silica catalyst at a temperature which will cause said paraffin to decompose into 9 a plurality of aromatic compounds in the presence of a catalyst and'which is at least 350 C., and for a contact time of less than 0.4 second, said diarylethane having at least one aryl group substituted with an alkyl group and a hydroxyl group. 5 2,375,756

JAMES KENNETH DIXON.

REFERENCES CITED The following references are of record In the 10 file of this patent:

OTHER REFERENCES Schelbley et al., Jour. Am. Chem. 800., vol. 62. 840-1 (1940), in Patent Omce Library. 

